Brilliant lichens reveal mammal perches

By Jeff Mitton

I ambled across Moraine Park in Rocky Mountain National Park, looking for something to catch my eye. In this portion of the park, small- to medium-sized boulders protruded from the ground. A small cone-shaped boulder, perhaps three feet tall, stood out from the others, for it was adorned by bright orange, almost red lichen.

I looked around, but could not see the culprit.

The elegant sunburst lichen, Xanthoria elegans,is highly tolerant of water-soluble forms of nitrogen, and this tolerance influences its distribution and abundance. Mammal urine contains urea, a molecule containing two atoms of nitrogen, and their feces also contain nitrogen. Birds release uric acid, a molecule containing four atoms of nitrogen, in a thick white paste that reveals nest sites on rocky cliffs.

The elegant sunburst lichen thrives at the burrow entrances of small mammals and conspicuously illuminates sentry posts where they sit vigilantly watching their territory. Orange lichens also identify hunting perches of birds and grow in profusion in seabird colony nesting sites.

The elegant sunburst lichen alerts naturalists to long-term haunts of small mammals. At the Notch, the highest point of Trail Ridge Road, extensive scree slopes drape from the road down into Forest Canyon. Pika alarm calls can be heard, but pikas are devilishly difficult to spot. However, bright orange lichens mark entrances to burrows and sites where pikas have surveyed their world for centuries and perhaps even millennia.

Sit quietly, a respectable distance away from the telltale lichen and you will exhaust the pika's timidity and patience. Pikas will soon resume haying, or gathering leaves and stems to accumulate a hay pile, the larder that will get them through the coming winter.

Elegant sunburst lichens also reveal places where yellow-bellied marmots linger and do what comes naturally. With binoculars, I have watched marmots sitting on cliffs high above Forest Canyon, enjoying a majestic vista from a sentry post marked by brilliant lichens.

The elegant sunburst lichen has an extraordinary range. It grows from wave-splashed marine shores to the peaks of high mountains and from the Arctic to the Antarctic. It grows on all continents except Australia.

Xanthoria elegansis currently recognized as a single species, but it varies markedly from place to place. In the Canadian Arctic its colors and the form and abundance of its reproductive structures vary regularly among habitats, suggesting that what we call the elegant sunburst lichen will eventually be recognized as several species.

Its extensive geographic range and its conspicuous color attracted the attention of lichenologists, archeologists and historians who use lichens to estimate the ages of rock surfaces. Lichens grow slowly, at relatively regular rates, so a lichen's size can be used to estimate its age and to make inferences about the duration that its foundation has been exposed. An elegant sunburst lichen takes one to two decades to become established and after that its radius increases by about 0.5 millimeters per year, or an inch in 50 years.

Who was the remorseless culprit who fertilized the rock in Moraine Park, encouraging brilliant lichens to grow?

The likely suspects include least chipmunks, golden-mantled ground squirrels and Wyoming ground squirrels.

Jeff Mitton (mitton@colorado.edu) is a professor in the Department of Ecology and Evolutionary Biology at the University of Colorado. This column originally appeared in the Boulder Camera.